Abstract This paper summarises the first eight months of monitoring of the PHA BONG photovoltaic generation project, a 500 kW p photovoltaic pilot plant, in Mae Hong Son province, Thailand. The local grid in this remote area in the North West of Thailand is very limited in its capacity and cannot be enlarged. It has been in operation since 20 March 2004 by feeding into 400 V AC, 22 kV medium voltage grid. The system consist of a photovoltaic array 1680 modules (140 strings, 12 modules/string; 300 W/module), power conditioning units and battery converter system. During the first eight months of this system's operation, the PV system generated about 383,274 kWh. The average of generating electricity production per day was 1695.9 kWh. It ranged from 1452.3 to 2042.3 kWh. The efficiency of the PV array system ranged from 9 to 12%. The efficiency of the power conditioning units (PCU) is in the range from 92 to 98%. The final yield ( Y F) ranged from 2.91 to 3.98 h/d and the performance ratio (PR) range from 0.7 to 0.9.